ⓘ Angular gyrus. The angular gyrus is a region of the brain lying mainly in the anterolateral region of parietal lobe, that lies near the superior edge of the tem ..

                                     

ⓘ Angular gyrus

The angular gyrus is a region of the brain lying mainly in the anterolateral region of parietal lobe, that lies near the superior edge of the temporal lobe, and immediately posterior to the supramarginal gyrus. Its significance is in transferring visual information to Wernickes area, in order to make meaning out of visually perceived words. It is also involved in a number of processes related to language, number processing and spatial cognition, memory retrieval, attention, and theory of mind. It is Brodmann area 39 of the human brain.

                                     

1. Function

The angular gyrus is the part of the brain associated with complex language functions i.e. reading, writing and interpretation of what is written. Lesion to this part of the brain shows symptoms of the Gerstmann syndrome: effects include finger agnosia, alexia inability to read, acalculia inability to use arithmetic operations, agraphia inability to copy, and left-right confusion.

                                     

1.1. Function Arithmetic and spatial cognition

Since 1919, brain injuries to the angular gyrus have been known to often cause arithmetic deficits. Functional imaging has shown that while other parts of the parietal lobe bilaterally are involved in approximate calculations due to its link with spatiovisual abilities, the left angular gyrus together with left Inferior frontal gyrus are involved in exact calculation due to verbal arithmetic fact retrieval. When activation in the left angular gyrus is greater, a persons arithmetic skills are also more competent.

                                     

1.2. Function Attention

The right angular gyrus has been associated with spatiovisual attention toward salient features. It may allocate attention by employing a bottom-up strategy which draws on the areas ability to attend to retrieved memories. For example, the angular gyrus plays a critical role in distinguishing left from right, by integrating conceptual understanding of the language term "left" or "right" with its location in space. Furthermore, the angular gyrus has been associated with orienting in three dimensional space, not because it interprets space, but because it may control attention shifts in space.

                                     

1.3. Function Default mode network

The angular gyrus is part of the default mode network, a network of brain regions activated during multi-modal activities that are independent of external stimuli.

                                     

1.4. Function Awareness

The angular gyrus reacts differently to intended and consequential movement. This suggests that the angular gyrus monitors the selfs intended movements, and uses the added information to compute differently as it does for consequential movements. By recording the discrepancy, the angular gyrus maintains an awareness of the self.

                                     

1.5. Function Memory retrieval

Activation of the angular gyrus shows that not only does it mediate memory retrieval, but also it notes contradictions between what is expected from the retrieval, and what is unusual. The angular gyrus can access both content and episodic memories and is useful in inferring from these the intentions of human characters. Furthermore, the angular gyrus may use a feedback strategy to ascertain whether a retrieval is expected or unusual.



                                     

1.6. Function Out-of-body experiences

Recent experiments have demonstrated the possibility that stimulation of the right angular gyrus is the cause of out-of-body experiences. Stimulation of the left angular gyrus in one experiment caused a woman to perceive a shadowy person lurking behind her. The shadowy figure is actually a perceived double of the self. Another such experiment gave the test subject the sensation of being on the ceiling. This is attributed to a discrepancy in the actual position of the body, and the minds perceived location of the body.

                                     

2. Clinical significance

Damage to the angular gyrus manifests as Gerstmann syndrome. Damage may impair one or more of the below functions.

  • Finger agnosia: inability to distinguish the fingers on the hand
  • Left-right disorientation
  • Dysgraphia/agraphia: deficiency in the ability to write
  • Dyscalculia/acalculia: difficulty in learning or comprehending mathematics
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